JLG 800A_AJ ANSI Service Manual - Manual (Page 156)

SECTION 3 - CHASSIS & TURNTABLE
3-100 – JLG Lift – 3120740
assembly keeps fuel available to the fuel injectors at a
constant pressure. A return line delivers unused fuel back
to the tank.
FUEL METERING SYSTEM PURPOSE
The basic function of the air/fuel metering system is to
control the air/fuel delivery to the engine. Fuel is delivered
to the engine by individual fuel injectors mounted in the
intake manifold near each intake valve.
The main control sensor is the heated oxygen sensor
(H02S) located in the exhaust system. The H02S tells the
ECM how much oxygen is in the exhaust gas. The ECM
changes the air/fuel ratio to the engine by control-ling the
amount of time that the fuel injector is "ON." The best mix-
ture to minimize exhaust emissions is 14.7 parts of air to 1
part of gasoline by weight, which provides the most effi-
cient combustion. Because of the constant measuring and
adjusting of the air/fuel ratio, the fuel injection system is
called a "closed loop" system.
The ECM monitors signals from several sensors in order
to determine the fuel needs of the engine. Fuel is deliv-
ered under one of several conditions called "modes." All
modes are controlled by the ECM. Refer to "Open Loop
and Closed Loop Operation" for more information.
FUEL PRESSURE REGULATOR
The fuel pressure regulator is a relief valve mounted in the
fuel filter. It provides a constant fuel pressure of 441 kPa
(64 psi).
If the pressure is too low, poor performance and a DTC 32
will set. If the pressure is too high, excessive odor and/or a
DTC 42 will result.
When replacing the fuel filter, be sure to use an identical
filter/regulator assembly. A standard fuel filter does not
Figure 3-56. Typical Fuel System
HIGH PRESSURE CIRCUIT - OPERATING PRESSURE 65 PSI.